1. Field of the Disclosure
The present version of these embodiments relate generally to the field of head designs for bolts or fasteners and more particularly to roof bolts or fasteners used in mining and tunneling underground.
2. Discussion of the Background Art
These embodiments relate to head designs for roof bolts, and more particularly to a novel head design for the head of bolts used generally in mines and underground digging. Generally when digging underground for mining and other purposes, the roof can become unstable and a many methods have been used to reinforce the roof or ceiling. The roof becomes unstable because the material for the tunnel has been removed. The material above the ceiling can cause the ceiling to crack and fall causing collapse of the tunnel. Many methods to reinforce the ceiling have been developed and practiced to help overcome this potentially dangerous problem.
One method of reinforcing the roof involves drilling a hole into the ceiling and inserting a bolt or rod with plate adjacent to the head to reinforce the ceiling. The shaft of the bolt can be threaded or have ribs along the length of the shaft and some shafts are smooth. The bolt head generally has some type of standard head design so that tools and equipment can attach to the head and drive the bolt. There is a washer element between the bead of the bolt and the shaft. The bolt can be very long depending upon the type of material in the ceiling. Miners and underground excavators like to see certain types of material in the ceiling above the tunnels so that bolls and plates can be most effective. Many times the preferred rock material for retaining the shaft to the rock is several feet from the ceiling, in some cases 6-8 feet or even more.
The bolt can be retained in the bole with the threads, with a mechanical anchorage device or can have a grout or adhesive that is inserted at various distances from the head or ceiling but generally at the top end of the hole. The distance for placement of the adhesive is determined by the type of rock that is found along the length of the hole. The adhesive can be placed at some appropriate distance from the head depending upon the type of material found at various elevations above the ceiling.
Many methods have been developed for securing the bolt in the hole. One method involves threaded rods and another involves two part adhesives. Another method involves pumping adhesives or grout through a bole in the shaft of the bolt. The two part adhesives are generally assembled in a separated two part cartridge which can be inserted into the hole before the bolt shah or along with the bolt shaft. When the bolt shaft is installed, the shaft is spun and this breaks the separation of the two materials in the cartridge and mixes them. The spinning of the bolt causes the adhesive to mix which results in a chemical reaction and results in the binding of the shaft to the rock with the adhesive. An upward force can also he given to the bolt head such that when the adhesive solidifies there is an upward force on the ceiling or the bolt is in tension.
The bolt or rod generally has a plate located adjacent to the washer element of the head of the bolt to disperse the loading of the bolt, head, washer and plate over the surface area of the ceiling adjacent to the plate. The bolt is installed so that the plate is as Slush with the ceiling as is possible. The bolt can then be forced upwards to create a tension in the bolt or various other methods have been developed to turn the bolt into the ceiling to tension the bolt. Other methods to tension the bolt either before and after the bolt has been inserted are known in the art. This loading from the bolt, head and washer is transferred to the plate and to the ceiling which compresses the ceiling to support the rock above the ceiling to deter collapse.
There are standards for the design and testing of roof bolts, shafts and heads, some of which are found in ASTM Designation F 432-04 “Standard Specifications for Roof and Rock Bolts and Accessories” and ASTM Designation F 606-90 “Standard Test Methods for Determining the Mechanical Properties of Externally and Internally Threaded Fasteners, Washers and Rivets”.
These standards specify tests to ascertain the minimum loading to which the roof bolts, heads, shafts and plates should withstand. While the products on the market generally meet the tests designed for roof bolts, failures still occur in the real world.
The applicant has seen cases where the washers of the bolt heads become loaded in an unbalanced manner. This is due to the fact that many times the holes in the ceiling are not drilled straight or the ceiling surface is not perpendicular to the holes and plate thereby does not sit parallel and adjacent to the ceiling surface. Other times the bolt is not driven exactly concentric to the hole center line when installed.
When any of these conditions occur, the washer is loaded at the washer plate interface more on one side of the washer than the other. When the load becomes too great, the washer regularly fails and this condition can result in failure of the head and shaft too. Subsequently, the plates can fall away from the ceiling. Failure of the bolt or plate support can result in the loss of ground support, ceiling dropping and possible collapse. If repair is possible it can be extremely costly. Work can stop until the tunnels or digging can be made safe from ceiling collapse.
While these bolts do meet the specifications for roof bolts, failures still occur. In other cases where the bolt load is perpendicular to the washer and plate in the ceiling, these bolts still fail at the washer head interface when the washers concave towards the head end of the bolt or shear from the bolt. The plate then fractures, bends or detaches from the holt head resulting in the ceiling lowering or possible collapse.
Applicants sought to change the head design to help prevent the failure of the bolt heads at the washer head interface and washer shaft interface. Applicant has modified the area on the shaft directly below the washer arid modified the head between the head end and the washer.
Testing has been performed and it has been found that these new embodiments are stronger by as much as 60% over the roof holt head designs in the background art.
For the foregoing reasons, there is a need for a new roof bolt head design or a dome headed roof bolt.